1. Field of the Invention
The present invention relates to the technology field of power electronic apparatuses, and more particularly to a synchronization signal transmitting device, a synchronization signal transmitting method and a power electronic apparatuses having the device.
2. Description of the Prior Art
In controlling a power electronic system, an identical synchronization clock signal with power frequency (called “power-frequency clock information” hereinafter) and/or a PWM carrier synchronization clock information (called “PWM carrier clock information” hereinafter) are provided to multi paralleled power electronic apparatuses so as to coordinate these apparatuses and enhance the electric power quality outputted by these apparatuses. Moreover, in the conventional power electronic system, an active detection method is commonly used for islanding detection in each of the power electronic apparatuses. To ensure the disturbance is added into each of the power electronic apparatuses coordinately, the disturbance information must be provided to each of them synchronously.
However, for a broad range-distributed power system, there are often long-distance (several hundred meters far at most) and strong electro-magnetic interference (EMI) among each other of different power electronic apparatuses, which lead to difficulty in reliably transmitting synchronization signal among multiple power electronic apparatuses. Accordingly, how to effectively transmit the synchronization signal under a harsh electromagnetic environment in a long-distance becomes an urgent issue to be resolved.
According to a conventional synchronization signal transmitting method for high power electronic apparatuses, a data frame from the information transmitter is transmitted to multiple paralleled processors at the receiver through CAN (Controller Area Network) buses or RS-485 buses. The data frame is a protocol data unit (PDU) of a data link layer (DLL) comprising frame header, data portion and frame end, wherein the frame header and the frame end includes essential control information, such as frame start information, addressing information and error control information, and the data portion includes the data to be transmitted such as synchronization information data.
After receiving the data frame, the processor at the receiver decodes, checks the data frame and makes time delay compensation to it, and thereby extract the synchronization signal from the data frame. If a data transmission error occurs due to EMI on CAN bus or on RS-485 bus, the processor can figure out the erroneous code by software verification and correct its effect on the synchronization signal. A reliable synchronization signal transmission is realized in this way.
However, the aforesaid method has the following shortcomings in spite of its enabling reliable synchronization signal transmitting by transmitting data frame on CAN bus or RS-485 bus:
(1) The aforesaid method may be used for transmitting the low frequency clock information such as power frequency of 50 Hz or 60 Hz, but cannot be used for transmitting high frequency PWM carrier clock information. The reason is that the Baud Rate used in the aforesaid method must be dozens times as high as the frequency of the transmitted synchronization clock information. Therefore, the necessary Baud Rate would be extremely high if the aforesaid method is used for transmitting the PWM carrier clock information (from several kHz to hundreds of kHz). For instance, when the PWM carrier has a frequency of 100 kHz, the necessary Baud Rate to transmit the data frame must be at least 5 Mbps. However, the CAN bus and/or the RS-485 bus are unable to accomplish such information transmission especially under a harsh electromagnetic environment in a long distance.
(2) The information transmission has very low time accuracy in the aforesaid method. In addition to receiving the synchronous clock signal, the processor at the receiver has many other programs to execute, for example, the high-priority interrupt program, the execution of which may affect the operation time of decoding and checking of the data frame. This would reduce the time accuracy of the transmitted synchronization clock information.
(3) The aforesaid method has a complicated adjustment of time delay compensation. From the aforesaid point (2), it may be known that a time delay of several milliseconds to hundreds of milliseconds may be caused due to execution of other programs. For this reason, the processor must make time delay compensation to the synchronization information. However, the execution time of software varies with the change of program code, which is not a constant, and this increases the difficulty and complicity in making time delay compensation to the synchronization signal.
(4) The aforesaid method has a high occupation to operating ability of the processors. From aforesaid points (2) and (3), in the aforesaid method the decoding, checking and time delay compensation of the data frame is mainly done by software, and thereby extracting the synchronization signal. However, with the frequency of the synchronization clock information increasing, the execution time of the used software become more inconstant, and hence a processor with higher operating ability is required, which leads to increased cost in processors.
Accordingly, in view of these shortcomings in conventional power electronic devices and method thereof, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a synchronization signal transmitting device, a synchronization signal transmitting method and a power electronic apparatus having the device.